1. Field of Invention
The invention concerns a synchronous flat belt drive according to the preamble of claim 1. It can be related to the IPC-classes F16H 7/02, F16H 55/30, and F16H 55/36.
2. Prior Art—The Story of the Invention
Since the mankind uses the technique for support of the daily life, it is confronted with friction. So, for example, more energy as fuel has to be supplied to an internal combustion engine, in order to obtain a predetermined performance, than is necessary according to the laws of thermodynamics. For, the movement of motor parts is inhibited by friction, and therefore a portion of the supplied fuel has to be spent for overcoming this friction, whereby heat is produced, which flows unused to the environment. Despite all inventions on the fields of electronics, of genetic engineering, or of nanotechnology we have obviously capitulated to the friction. Instead we try to reduce it, by providing, for example, as naturally almost like a law of nature our machines with lubricants. Thereby we have apparently lost sight of simple solutions of mechanics, although the man gladly uses them as the rocking horse at his first years of age, and as the rocking chair in the later years of age. It is the principle not to slide along on a surface, but instead to roll on a surface.
Here the invention starts. The objective is, rollingly transmitting a rotational movement at our machines.
Erroneously, often it is assumed, that a face gear, for example having an involute tooth system, as it is found in a large dissemination, for example, in the vehicle gearboxes, performs such a rolling movement. Unfortunately, this is not the case, for otherwise we could at least save the gearbox oil. With a slow motion simulation of the movement (see http://de.wikipedia.org/wiki/Bild:Involute_wheel.gif), which a tooth performs engaging in the opposing tooth system, one can easily recognise, that initially the tooth slides into along the opposing tooth, then rolls at the rolling circle, and afterwards again slides out along the opposing tooth. Thereby surface damages are produced on the teeth (Pitting). A rolling movement is only performed at the rolling circle. It is this circle, on which the tool rolled for forming the tooth system. Above and below the rolling circle there occurs a sliding with the generating of the energy consuming dynamic friction.
As a logical consequence, therefore it is proposed, letting a tooth engaging a tooth system of an opposing tooth, which only exists at the rolling circle. One can well imagine this at a gear rack, which is reduced to a thin layer around the rolling line. At the first glance, such a construction seems firstly not to be feasible, for an opposing tooth with such a small extension in tooth height direction would barely have the necessary strength (buckling), in order to withstand the force of the meshing tooth. Moreover, how the force in the gear rack or the gear should be transmitted. Here the next inventive step constitutes. The thin tooth system layer is not formed as compression receiving member, but as tension member. And, as is generally known, thin layers are able to transmit heavy tension loads. Nevertheless, here also occurs the problem of transmitting the force, which is applied by a meshing tooth to the opposing tooth system.
In a next inventive step, therefore the tension layer is flexibly formed, and is guided about a gear. However, such a guided tension layer would wedge in the tooth system by applying of tension force at its ends, whereby again friction would occur. This has to be prevented, namely, the flexible thin opposing tooth system layer has to be guided in a defined distance to the shaft of the gear. This defined distance is realized at a normal opposing gear by means of the bearing of this opposing gear. However, such a bearing is not possible for the thin flexible opposing tooth system layer. Here, the next inventive step constitutes. Namely, this support function is performed in a radial direction by means of cylindrical discs having a predetermined same diameter and a predetermined width, which are applied on both sides of the gear, directly adjacent to the gear, and coaxially to the shaft of the gear. Thereby the diameter is determined such, that it is greater than the foot circle diameter of the tooth system of the gear. So now, with applying of tension force at its ends, this thin flexible opposing tooth system layer can support in radial direction on the cylindrical peripheral surfaces on both sides adjacent to the gear, and performs at a circulation around the gear a purely rolling movement.
Now the problem of transmitting the force, which is applied from a meshing tooth to the opposing tooth system, can be solved. Namely, the thin opposing tooth system layer supports directly adjacent to the rolling cylinder, which is defined by the peripheral surfaces of the cylindrical discs to be adjacent to the gear, tangentially to this rolling cylinder on the tooth system of the gear. Namely, along the total winding circumference between the thin flexible opposing tooth system layer and the rolling cylinder, which is defined by the peripheral surfaces of the cylindrical discs. Unlike with the meshing of two gears the force is with the meshing of a gear together with a thin flexible opposing tooth system layer not pointwise transmitted between two teeth, but by means of a series of support lines, which the thin flexible opposing tooth system layer forms together with the tooth system of the gear along the winding circumference. Namely, each tooth of the gear pushes in movement direction of the gear along the winding circumference a tooth of the thin flexible opposing tooth system layer forward like a pulling horse its breast belt. A tooth of the gear newly coming in engagement contacts a tooth of the thin flexible opposing tooth system layer firstly, when with sidewise viewing of the gear a line, which is running from the centre of the gear through the symmetry axis of the newly in engagement coming tooth, is perpendicularly aligned to the thin incoming straightened flexible opposing tooth system layer. From here, the new tooth forms a support line, which is adjacent to the rolling cylinder and is aligned parallel to the axis of the rolling cylinder (with a spur gear tooth system). However, the tooth newly coming in engagement has to bear the load not alone, but shares the load together with the other pulling teeth along the winding circumference like the individual acting persons at a rope pulling.
By forming such pairings of gear and adjacent cylindrical discs on the one side and of a thin flexible opposing tooth system layer on the other side one can transmit rotation movements purely rolling.
Using such pairings for a purely rolling movement transmission, for example, for driving a camshaft by a crankshaft, both the cylindrical discs on both sides of a gear and the gear can be firmly connected to a shaft. For an application in a controlling gearbox, the cylindrical discs on both sides of a gear in a further inventive step, for example, can be firmly connected to a shaft, and the gear can be in a controllable form joint manner connected to a shaft. Thereby can the gears not yet being in the force flow with a shaft (controllable form joint connection not yet established) run on this shaft driven by the thin flexible opposing tooth system layer like in an idling, whereby a later coupling is simplified.
To be honest, the invention is not yet complete until hither. For, this thin flexible opposing tooth system layer has naturally to be bent at a circulation, and thereto deformation energy is necessary. Therefore, it would be all efforts made so far for avoiding the dynamic friction in vain, if now the saved fuel had to be applied as energy for deformation of the thin flexible opposing tooth system layer. Here, my experience with the construction of wings consisting of laminated layers of carbon fibre composite material could surprisingly provide further assistance. Namely, an initially limited damage, barely visible from outside, can evolve by an impact action on such a laminated layer to a catastrophic failure for the aircraft, by delaminating the layer configuration with the operating load starting from the initially limited damage position on a large area with the progressing time, and finally leading to a failure of the wing structure.
The reason for this one can understand with a small mathematical consideration. Namely, the geometrical moment of inertia of a homogeneous layer with a thickness t0 and a width b0 amountsI0=b0·t03/12;on the other hand, the geometrical moment of inertia of a layer, which in turn consists of individual not to each other connected individual thin layers, each with a thickness t=t0/n (n=2, 3, 4, . . . ) (with n thin individual layers) and a width b0 for a single thin layer of the n layers, amountsIn=b0·(t0/n)3/12;and further, the total geometrical moment of inertia of a layer of n individual thin layers amountsI=n·In=n·b0·(t0/n)3/12=I0/n2;that is, when a layer with identical total thickness t0 is produced instead from a homogeneous layer from, for example, 10 individual thin not to each other connected layers (n=10), then this total layer surprisingly has a lower geometrical moment of inertia by the factor 100, which in turn results as product together with the modulus of elasticity E the bending stiffness. That is, a delaminated wing has only a small fraction of the original bending stiffness, and inevitably has to fail.
As catastrophic as this effect is with a wing, the more pleasant is this effect with a thin flexible opposing tooth system layer. For, since the magnitude of the deformation energy necessary to be applied at a circulation of a thin flexible opposing tooth system layer is proportional to the magnitude of the bending stiffness, by forming the thin flexible opposing tooth system layer from in turn n individual thin layers with identical total thickness the deformation energy necessary for a circulation can be reduced to a small fraction equal 1/n2 of the original value (n=1).
Moreover it is known, that thin layers, particularly metal layers, can be formed by cold rolling with a high tensile strength. That means, the thin flexible opposing tooth system layer of in turn n individual thin layers runs not only almost without the need of deformation energy, but also a thin flexible opposing tooth system layer of in turn n individual thin layers surprisingly has a higher tensile strength with identical total thickness of the thin flexible opposing tooth system layer than an embodiment having one layer. Thereby, either the total thickness of the thin flexible opposing tooth system layer of in turn n individual thin layers can be reduced compared to the calculated value for an embodiment having a single layer, or the safety factor for the tensile strength can be increased.
Now, by these elements of the invention, here described, gear boxes, primary drive systems, secondary drive systems, and couplings, et cetera, according to the invention can be modified.
Further, for a commercial world-wide use it is important, that the invention can be well integrated in the already existing cosmos of the machine elements. Therefore, it is advantageously, using as gears, which engage in the thin flexible opposing tooth system layer, already established standardised gears.
Therewith the story of the present invention is told. Still additional inventive elements are described in the following.
Discussion
Now, the discussion with the prior art takes place. Therefore, in the following the thin flexible opposing tooth system layer is referred to as flat belt having a series arrangement of apertures, and in the following the tooth system of the gear is referred to as series arrangement of projections, and the cylindrical discs, which are adjacent on both sides to a gear, are referred to as pulleys.
Synchronous flat belt drives are in the drive technology for the synchronous transmission of rotation movements widely spread. They substantially consist of at least one cylindrical drive pulley and at least one cylindrical driven pulley, one flat belt in an opened or closed construction and a tensioning device for the flat belt, whereby the flat belt forms together with the pulleys as a result of the static friction force, which acts along the winding circumference between the flat belt and the respective pulley, a friction force joint connection, and whereby the flat belt forms together with the pulleys as a result of the engaging of a series arrangement of apertures on the flat belt in a series arrangement of projections on the respective pulley along the winding circumference between the flat belt and the respective pulley additionally to the above mentioned friction force joint connection a form joint connection.
Synchronous flat belt drives have compared to other synchronous drives, such as a roller chain drive and a tooth belt drive, the following advantages: a low noise emission due to an aerodynamically smooth surface of the flat belt, low production costs due to a simple construction of the flat belt, and no polygon effect due to the support of the flat belt on a cylindrical pulley working surface.
Nevertheless, until today synchronous flat belt drives have found no large dissemination, since with the known synchronous flat belt drives the rolling pairing of a flat belt aperture and a pulley projection enables no purely rolling. Thereby, at an operation of the synchronous flat belt drive friction losses and an increased wear occur. Furthermore, the circulating flat belts are not formed of individual thin separated layers, whereby a high deformation energy has to be spent at a circulation.
Particularly, the synchronous flat belt drives apply according to the U.S. Pat. No. 1,683,955 (Sep. 11, 1928), U.S. Pat. No. 2,408,666 (Oct. 1, 1946), U.S. Pat. No. 3,642,120 (Feb. 15, 1972), U.S. Pat. No. 3,772,930 (Nov. 20, 1973), U.S. Pat. No. 4,568,320 (Feb. 4, 1986), WO 86/01570 (Mar. 13, 1986) and U.S. Pat. No. 5,129,865 (Jul. 14, 1992) projections having a circular cross section, whereby by means of these projections beside the synchronisation function also the function of the lateral guidance of the flat belt is assumed. Moreover, between the individual projections in circumference direction of the pulley the flat belt radially supports to a pulley axis on the respective pulley working surface. By both operations, particularly at the getting into of an aperture in a projection and at the getting off of an aperture from a projection, friction forces are generated. By these friction forces the efficiency factor of the flat belt is reduced, and a wear is caused both at the projections and at the apertures. Furthermore, the wear debris caused by the friction forces directly accumulates in the foot area of a projection on the pulley working surface. This reduction of the effective height of a projection can lead together with a widening of the aperture by the wear to a non-engaging of an aperture in a projection, whereby the flat belt is further damaged, and it comes to a failure of the synchronisation.
Further, the flat belts with the known synchronous flat belt drives are not formed in a layer configuration of at least one strip having several layers, whereby a higher bending stiffness and a lower strength with identical total thickness of the flat belt are obtained. Thereby, a efficiency factor benefit is not realised, because at a circulation of a flat belt of a single layer a clearly higher deformation energy has to be spent than at a circulation of a flat belt of several layers with identical total thickness of the flat belt.
Further, the synchronisation with the known synchronous flat belt drives is not controllable. Thereby, it is not possible, in a run up phase or a run down phase, or during the operation of the synchronous flat belt drive to turn off or to turn on the synchronisation.
Further, the known synchronous flat belt drives are not standardised, and also can not be integrated in the standardisation system of the machine elements of the drive technology.